meson: avoid using replace() to not unnecessarily bump meson >= 0.58.0

Debian bullseye ships with meson 0.56.2 which is too old to understand
replace().

Work around that with split() and string concatenation.

Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Closes: #16
Signed-off-by: Sam James <sam@gentoo.org>

man/meson.build

@@ -19,7 +19,7 @@ fs = import('fs')
 out_pages = []
 generated_man_pages_exist = true
 foreach page : pages
-  man_page_name = page.replace('.docbook', '.1')
+  man_page_name = page.split('.')[0] + '.1'
   out_pages += man_page_name
   if not fs.exists(man_page_name)
       generated_man_pages_exist = false